1. Field of the Invention
The present invention relates to a finisher, and more particularly to a finisher which punches sheets ejected from an image forming apparatus.
2. Description of Related Art
In recent years, various kinds of sorters (finishers) for sorting image-formed sheets have been developed as optional attachments for image forming apparatuses such as electrophotographic copying machines and laser printers.
Some of these finishers have a function of stapling sheets and/or a function of punching sheets as well as a function of sorting sheets.
As for punching mechanism, there are two types: a type which punches sheets one by one while the sheets are being transported; and a type which punches a stack of sheets after sorting at a time. The former single punching type, as disclosed by Japanese Patent Laid Open Publication No. 4-129699, has a plurality of punching rods, and all the punching rods are driven simultaneously to punch a sheet.
However, the number of punch holes to be made in a sheet varies. For example, in the U.S.A., making two holes or three holes in a sheet is required according to the sheet size. The punching mechanism disclosed by the above-mentioned Japanese Publication, however, is for exclusive use to make two holes or to make three holes. Therefore, the operator must exchange punching units to attach one which makes a desired number of holes, which is troublesome. As for the latter stack punching type, it is well-known that a punching unit is moved in parallel to one side of a stack of sheets and stopped at specified positions on the way to make holes. However, this type of punching unit including its driving means is large, and the process speed is low.
Further, as for a finisher with which an operator selects a desired punch operation mode, the selecting operation is complicated, and there is fear that misselection may occur.